Iron-nickel alloys



Feb. 27, 1968 E. JOSSO IRON-NICKEL ALLOYS Filed Nov. 15. 1966 Unite Sttes 3 Claims. (51. 75-1225 ABSTRACT (IF THE DlISQLOSURE Iron-nickel alloys having improved magnetic properties and improved forgeability are obtained by replacing manganese in the alloy by uranium. The nickel content is greater than or equal to 30% and the amount of uranium is from 0.02 to 0.5% by Weight.

This invention relates to uranium-containing iron-nickel alloys.

It is well known that vacuum-melted iron-nickel alloys having a nickel content greater than or equal to 30% have excellent magnetic properties. Deoxidised alloys of this kind can be forged and hot-rolled without difliculty if they are prepared from very pure raw materials, but they behave differently if the raw materials used contain sulphur, as is frequently the case with commercial quality materials. The magnetic properties remain substantially unchanged, but the high-temperature deformability deteriorates unless a desulphurising agent is added to the alloy; unless this is done, the product cannot be forged or hot-rolled and despite its good magnetic properties it can be used only for very restricted applications.

To overcome this difiiculty, conventional practice is to add a small quantity (for example 0.3-0.5%) of manganese to the melt in order to facilitate forging or hotrolling of the ingots.

Unfortunately, this addition of manganese, which combines with the sulphur to give a relatively stable sulphide, has an unfavourable eifect on the magnetic properties of the alloy, as Will be apparent from the following table, which relates to 0.3 mm. thick strip rings originating from three melts prepared under identical conditions with the same raw materials.

TABLE 1 atent The carbon contents shown in Table I were determined on the ingot prior to any conversion operations. These relatively high contents have the effect or" keeping the oxygen concentration of the matreials at a very low level of about 10 ppm. After rolling into thin strips and after annealing for 6 hours at 1100 C. in purified hydrogen to develop the magnetic properties, this carbon content drops to about 0.01%.

It is well known that uranium has a great afiinity for sulphur and oxygen. In steel it forms refractory inclusions of a globular shape which are thought to be oxysulphides.

Work on the use of uranium in ferrous alloys has hitherto been devoted to ordinary, alloy or stainless steels solely to improve their mechanical properties. Uranium increases the tensile strength at ambient temperature, increases quenchability and promotes structural hardening. With regard to resistance of stainless steels to corrosion, the results are as yet too incomplete for any definite conclusions to be drawn.

No coherent data is available on the influence of an additional of uranium to binary or complex iron-nickel alloys having a nickel content greater than 30%, such alloys being in widespread use because of their special physical properties (their magnetic, expansion, electrical, mechanical and thermomechanical properties in particular).

Tests have shown the advantage of uranium over mag- It has been foundand this is one of the features of the invention-that uranium may advantageously completely or partly replace manganese in order that ironnickel alloys having a nickel content greater than or equal to 30% may be made forgeable.

This improvement of forgeability is obtained by the use of uranium as desulphurising agent and contrary to previous tests it is advantageous to introduce it into material which has previously been satisfactorily deoxidiscd in order to prevent some of the uranium from being neutralised in the form of an oxide.

It is therefore advantageous for the oxygen concentration not to exceed 100 ppm. Processing partially or completely in vacuo or in a protective or reducing gas may be of advantage to give such a low impurity content.

Reference No. Chemical analysis of ingot, percent Permezzhility a 5 milloersteds 1 (with manganese)- S =0.0088, 3, 560

O =0.00 C =O.l31,

2 (with manganese)- S =0.008 4, 170

3 (without manganese). S =0.0090, 9, 440

Maximum Coercivity, permeability 0e.

A heat treatment was carried out and comprised annealing for 6 hours at a temperature of 1100 C. in hydrogen. The first two melts respectively contained about 0.5 and 0.3% of manganese while the third contained only traces thereof. Although the third melt was unfortunately unforgeable, it had very much better magnetic properties than the first two.

TABLE IL-CHEMICAL ANALYSES (PERCENTAGES, UNLESS OTHERWISE INDICATED) Reference C Si Mn S P N i O 2 N Addition (up (p-p- 0.03 0.0090 0.008 48.98 10 19 None.

( 0.34 0.0089 0.005 49.50 5 7 Mn:0.34. 0.09 0.0078 0.005 48.98 6 6 U:0.05. 0.0073 0.007 49.15 U:0.10. 0.0067 0.007 49.20 U:0.25.

l Traces.

The deformability of the ingot without a desulphurising addition is practically zero between 500 and 800 C.; above 800 C. it improves, but never reaches a satisfactory level. With an 0.3% manganese addition, the fragil- Of course the above-indicated uranium contents are 2 given by way of example and have no limiting force. The

Here again the compositions are given by way of example and have no limiting, force. The nickel content is preferably between 43 and 55% for the application in question but the superior magnetic quality provided by uranium instead of manganese may be obtained with all ferronickel alloys having a nickel content greater than or equal to Table IV gives examples of results obtained with melts containing various nickel contents. The corresponding properties were measured on 0.07 mm. thick strip rings annealed for 6 hours at 1100 C. in hydrogen with slow cooling in the furnace in the case of the alloy containing 36% of nickel; in the case of the alloy containing 78% of Ni, the tests were carried out on 0.3 mm. thickstrip rings annealed for 6 hours at 1000 C. in hydrogen with rapid cooling from 600 C.

TABLE IV S-content Mn-content U-contont Permeability Maximum Coercivity, Type of alloy by weight by weight by weight at 5 moe. permeability Oersteds Percent Percent Percent Fe-Ni alloy containing 36% of Ni 0. 01 0.8 2, 100 9,000 0.20

Fe-Ni alloy containing 78%0! Ni 0. 007 0. 48 8, 000 62, 000 0. 09

beneficial eiiect of uranium is found with an addition of as little as 0.02% by Weight; with regard to the top uranium concentration limit, this is dictated more by safety requirements in respect of radiation than by technological conditions. The maximum concentration would be limited to 0.5% by weight. Similarly, although Table II and the single figure refer essentially to alloys containing 48-50% Ni, these contents have no limiting force and the beneficial influence of the uranium additive covers all ferronickel alloys having a nickel content greater than or equal to 30%.

It has also been found-and this is another feature of the inventionthat for equal forgeability, the uranium additive is much less harmful to the magnetic properties than is the manganese additive. This is clear from Table III, which shows the magnetic properties after annealing for 6 hours at 1100 C. in hydrogen for iron-nickel alloy melts containing 48 to 50% Ni processed under identical conditions and respectively containing 0.34% Mn, 0.05% U, 0.10% U and 0.25% U.

TABLE III Magnetic properties Reference Addition Permability Maximum Coercivit-y,

at 5 milli- Permeability 0e.

oersteds The main object of the invention is to replace manganese by uranium in magnetic iron-nickel alloys. However, since the improved foreability provided by uranium is valid irrespective of the use for which the material is intended, the field of application of the invention is not restricted solely to magnetic alloys but relates generally to all binary or complex iron-nickel alloys having a nickel content greater than or equal to 30%, irrespective of use (e.g., magnetic alloys, alloys having a specific expansion, alloys having special elastic or thermoelastic properties, alloys having a specific resistivity, and so on). By complex iron-nickel alloys is meant iron and nickel based alloys which in addition to the impurities inherent in any metallurgical product contain additions of chromium, copper, silicon, molybdenum, aluminum, calcium, or magnesium for example which, without modifying the character or structure of the alloy, contribute towards improving the physical properties thereof.

I claim:

1. Binary iron-nickel alloys, having a nickel content at least equal to 30% by weight, 0.02 to 0.5% by weight of uranium and the remainder iron with the conventional impurities of metallurgical products.

2. Iron-nickel alloys as described in claim 1, containing less than p.p.m. of oxygen.

3. Iron-nickel alloys as described in claim 1, the nickel content by weight being between 43 and 55%.

References Cited UNITED STATES PATENTS 9/1964 Douglas et a1. 75122.5 9/1966 Weber 75-122.5 X 

